1. Field of the Invention
The present invention relates to a normally closed-type fluid control valve for controlling a flow rate and a pressure of various kinds of fluid such as gases and liquids.
2. Description of the Prior Art
This kind of normally closed-type fluid control valve (hereinafter referred to as the valve) has been disclosed in for example Japanese Patent Application Laid-Open No. Sho 64-55487. It is shown in FIG. 4(A), (B).
Referring to FIG. 4(A), (B), reference numeral 51 designates a valve base comprising an inlet port 52 provided on the left side thereof, a vertical passage 53 communicating with said inlet port 52 provided at a center thereof, an upward opened fluid chamber 56 housing a diaphragm 55 fixed by means of a diaphragm counter member 54 provided in an upper portion thereof, an outlet port 57 communicating with said fluid chamber 56 provided on the right side thereof, an orifice 58 formed in an upper portion of said vertical passage 53 and a valve seat 59 formed around said valve mouth 58. Reference numeral 60 designates a cylindrical member standing on an upper surface of said valve base 51 so as to push down said diaphragm counter member 54 from outside of the diaphragm counter member 54 and it is fixed by means of a cylindrical counter member 62 fixedly mounted on said upper surface of the valve base 51 by means of bolts 61.
Said cylindrical member 60 is provided with a valve rod 63 standing therewithin under the condition that a lower end surface of said valve rod 63 is brought into contact with an upper surface of a central portion of said diaphragm 55. And, a pressing spring 65 for energizing the valve rod 63 downward is provided between an upper stepped portion 64 of the valve rod 63 and an upper inner surface of the cylindrical member 60 so that the diaphragm 55 may be normally engaged with said valve seat 59 to normally close said orifice 58 and thus normally close the valve by pressing the valve rod 63 in the direction of the diaphragm 55 by means of said pressing spring 65. In addition, the valve rod 63 is provided with a through hole (not shown) in a lower portion thereof. A bridge 66 inserted through said through hole and placed on an upper surface of the diaphragm counter member 54 is provided with a piezostack 67 comprising a large number of piezoelements laminated on an upper surface thereof so that the valve rod 63 may be lifted by the action of said piezostack, whereby the pressing spring 65 is compressed to separate the diaphragm 55 from said valve seat 59 and open the orifice 58 and thus the valve is opened.
In the valve having the above described construction, it is not required to provide moving members, such as the pressing spring 65 and an adjustable screw 68, within a fluid passage such as the fluid chamber 56, so that an effect occurs in that the production of metallic powders resulting from the contact among metals in the fluid passage can be prevented and thus an inside of the valve base 51 and a fluid can be prevented from being contaminated and damaged.
However, in the above described conventional valve, the piezostack 67 has not the so-called closed type construction, so that a problem occurs in an insulation. And, a disadvantage occurs in that if it is intended to give the piezostack 67 a tightly closed construction, it is large-sized. In addition, the pressing spring 65 for energizing downward the valve rod 63 is provided between said upper stepped portion 64 of the valve rod 63 and said upper inner surface of the cylindrical member 60, so that a lead wire 69 for supplying the piezostack 67 with a voltage can not be taken out from above the piezostack 67 but can be taken out from the side portion of the piezostack 67. A disadvantage occurs in that an insulating construction for taking out said lead wire 69 is complicated and as a result this kind of valve is large-sized.